Method for increasing the reactivity of lignin

ABSTRACT

The present invention relates to a method for increasing the reactivity of lignin, wherein the method comprises the following steps: a) forming, under heating at a temperature of 30-70° C., an aqueous dispersion comprising alkali and lignin, wherein the alkali comprises a hydroxide of an alkali metal; and b) heating the dispersion formed in step a) at a temperature of 50-95° C. for producing alkalated lignin.

FIELD OF THE INVENTION

The invention relates to a method for increasing the reactivity oflignin and to the further use of such lignin.

BACKGROUND OF THE INVENTION

Lignin is a natural polymer, which can be extracted from e.g. wood. Aslignin is a natural biopolymer its use as a component in glues insteadof synthetic materials has been investigated in order to come up with amore environmentally friendly adhesive composition. Especially, theability to replace synthetic phenol in phenolic resins, such as phenolformaldehyde resin, has been the object of prior art.

Different types of adhesive compositions, such a phenolic glues, can beused with wood products. Examples of such glues include compositionscomprising phenol formaldehyde resin. Traditionally synthetic phenolformaldehyde resins are produced by polymerizing phenol and formaldehydein the presence of a catalyst. Examples of such catalysts are sodiumhydroxide (NaOH) and acids. The method for producing phenol formaldehyderesin comprises adding formaldehyde in a stepwise manner to a phenolcomposition and thereafter rising the temperature of the formedcomposition up to 80-90° C. The composition is cooked at thistemperature until a desired viscosity of the formed resin or polymerchain length is reached.

Lignin can be used for the purpose of decreasing the amount of syntheticphenol in a resin composition. Lignin has previously been used forreplacing phenol during the production of lignin-phenol-formaldehyderesin.

It has been possible to replace up to 30% of the synthetic phenol in thefinal resin, e.g. phenol formaldehyde resin, with lignin, but higherreplacement results in unsatisfying properties of the produced glue.

The inventors have therefore recognized a need for a method, which wouldresult in a higher phenol replacement in the composition and thus in amore environmentally friendly binder composition having suitableproperties for use in different applications.

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new method for increasingthe reactivity of lignin. Further, the purpose of the invention is toprovide a new type of method, where the more reactive lignin is used forreplacing at least part of the amount of synthetic materials used duringthe production of a binder composition. Especially the purpose is toproduce a more environmentally friendly binder composition to be usede.g. in adhesive applications.

SUMMARY

The method for increasing the reactivity of lignin according to thepresent invention is characterized by what is presented in claim 1.

The lignin obtainable by the method according to the present inventionis characterized by what is presented in claim 12.

The method for producing a binder composition according to the presentinvention is characterized by what is presented in claim 13.

The binder composition according to the present invention ischaracterized by what is presented in claim 18.

The adhesive composition according to the present invention ischaracterized by what is presented in claim 19.

The uses according to the present invention are characterized by what ispresented in claims 20 and 21.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and constitute a part of thisspecification, illustrate some embodiments of the invention and togetherwith the description helps to explain the principles of the invention.In the drawings:

FIG. 1 is a flow chart illustration of a method for increasing thereactivity of lignin and of the use of lignin having increasedreactivity according to one embodiment of the present invention;

FIG. 2 shows the result of differential scanning calorimetry (DSC)measurement of a binder composition (resin) produced by using ligninalkalated in accordance with the present invention; and

FIG. 3 shows the result of DSC measurement of a binder composition(resin) produced by using lignin treated in accordance with comparativeexample 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for increasing the reactivityof lignin, which method comprises the following steps:

a) forming, under heating at a temperature of −70° C., an aqueousdispersion comprising alkali and lignin, wherein the alkali comprises anhydroxide of an alkali metal; and

b) heating the dispersion formed in step a) at a temperature of 50-95°C. for producing alkalated lignin.

A drawback of different methods for separating or isolating lignin frome.g. biomass is that the lignin is condensed during the procedure due tothe low pH environment used. Thus, separated lignin has a rather lowreactivity and a heterogenic nature, which affect the reactions withother reactant components during e.g. the production of a bindercomposition. The low reactivity of lignin has been one of the reasonspreventing a higher replacement level of e.g. synthetic phenol in bindercompositions with biobased lignin. It has been recognized that theproperties of currently available binder compositions, wherein up to50-60% of the synthetic phenol has been replaced with lignin, are notacceptable for e.g. gluing applications. E.g. the strength of gluedjoints has not been on a required level.

The inventors surprisingly found out that the reactivity of lignin canbe increased by the method of the present invention and further that ahigher replacement level of e.g. synthetic phenol in binder compositionscan be achieved when using this kind of activated lignin during theproduction of the binder composition.

The expression “lignin having increased reactivity” should be understoodin this specification, unless otherwise stated, as referring to lignin,which has been treated by the method according to the present invention.Treating the lignin with the method according to the present inventionactivates the lignin making it more suitable for use in furtherapplications. The reactivity of lignin is thus increased compared tolignin, which has not been treated by the method according to thepresent invention.

In this specification, unless otherwise stated, the expression “lignin”should be understood as any lignin suitable to be used in the presentinvention.

Lignin may include essentially pure lignin as well as lignin derivativesand lignin modifications.

By the expression “essentially pure lignin” should be understood as atleast 90% pure lignin, preferably at least 95% pure lignin. In oneembodiment of the present invention the essentially pure lignincomprises at most 10%, preferably at most 5%, of other components.Extractives and carbohydrates such as hemicelluloses can be mentioned asexamples of such other components.

In one embodiment of the present invention the lignin to be treated bythe method according to the present invention is selected from a groupconsisting of kraft lignin, biomass originating lignin, lignin fromalkaline pulping process, lignin from soda process, lignin fromorganosols pulping and combinations thereof.

Different lignin components may have different properties, e.g.molecular weight, molar mass, polydispersity, hemicellulose andextractive contents. In one embodiment of the present invention thelignin includes water but no solvent.

By “kraft lignin” is to be understood in this specification, unlessotherwise stated, lignin that originates from kraft black liquor. Blackliquor is an alkaline aqueous solution of lignin residues,hemicellulose, and inorganic chemicals used in a kraft pulping process.The black liquor from the pulping process comprises componentsoriginating from different softwood and hardwood species in variousproportions. Lignin can be separated from the black liquor by different,techniques including e.g. precipitation and filtration. Lignin usuallybegins precipitating at pH values below 11-12. Different pH values canbe used in order to precipitate lignin fractions with differentproperties. These lignin fractions differ from each other by molecularweight distribution, e.g. Mw and Mn, polydispersity, hemicellulose andextractive contents. The molar mass of lignin precipitated at a higherpH value is higher than the molar mass of lignin precipitated at a lowerpH value. Further, the molecular weight distribution of lignin fractionprecipitated at a lower pH value is wider than of lignin fractionprecipitated at a higher pH value. Thus the properties of the lignin canbe varied depending on the end use of the gluing application.

The precipitated lignin can be purified from inorganic impurities,hemicellulose and wood extractives using acidic washing steps. Furtherpurification can be achieved by filtration.

In one embodiment of the present invention the dry matter content of thelignin is below 98%, preferably 40-80%, and more preferably 50-70%.

In one embodiment of the present invention the lignin is separated frompure biomass. The separation process can begin with liquidizing thebiomass with strong alkali followed by a neutralization process. Afterthe alkali treatment the lignin can be precipitated in a similar manneras presented above. In one embodiment of the present invention theseparation of lignin from biomass comprises a step of enzyme treatment.The enzyme treatment modifies the lignin to be extracted from biomass.Lignin separated from pure biomass is sulphur-free and thus valuable infurther processing.

The alkali comprises a hydroxide of an alkali metal. In one embodimentof the present invention the alkali is selected from a group consistingof sodium hydroxide, potassium hydroxide and mixtures thereof. In oneembodiment of the present invention the alkali is sodium hydroxide.

In one embodiment of the present invention the concentration of alkaliis 5-50 weight-%, and preferably 10-25 weight-% based on the totalweight of the dispersion in step a).

In one embodiment of the present invention the concentration of ligninin step a) is 10-50 weight-%, preferably 20-50 weight-%, and morepreferably 20-45 weight-% based on the total weight of the dispersion instep a).

In one embodiment of the present invention the temperature in step a) ispreferable 50-65° C.

In one embodiment of the present invention the temperature in step b) ispreferable 60-75° C.

In one embodiment of the present invention step b) is carried out for 15minutes-24 hours, preferably for no longer than 5 hours, and morepreferably for 0.5-1.5 hours.

The method according to the present invention, and especially thealkalation steps a) and b) result in the lignin being activated. Asabove discussed, lignin is condensed during acidic isolation orseparation processes. Without limiting the invention to any specifictheory about why alkalation of lignin results in a more reactive ligninbeing formed, it is to be considered that the alkalation opens themacromolecular structure of lignin whereby the steric hindrances thatusually disable reactive groups in lignin structures are removed.Alkalation may also add charged groups to the lignin macromolecule. Theadvantage of using alkalated lignin e.g. for producing a bindercomposition is that the compatibility and reaction behavior is muchbetter than in a normal case, where non-treated lignin has been used inthe cooking or polymerizing stage.

In one embodiment of the present invention the method comprises, beforestep a), the step i) of reacting lignin with a compound selected fromthe class of phenols. In one embodiment of the present invention thecompound is selected from a group consisting of phenol, cresol,resorcinol and combinations thereof. In one embodiment of the presentinvention the compound is phenol. Allowing the aliphatic part of ligninto react with e.g. phenol increases the number of phenolic OH-groupsattached to the aliphatic part of lignin. As the number of OH-groupsincreases the reactivity of lignin during e.g. the cooking step of abinder production method with the other reactant components isincreased. The advantage of alkalating phenotated lignin is that inaddition of having new phenolic OH-groups attached to the lignin thelignin structure will be opened as above discussed. The increasedreactivity of lignin has the advantage of enabling to replace a higheramount of synthetic reactants such as phenol with biobased lignin in thefinal binder composition.

In one embodiment of the present invention step i) is carried out at atemperature of 100-140° C. for 1-3 hours in the presence of a catalyst.In one embodiment of the present invention the catalyst used in step i)is an acid, preferably sulphuric acid (H₂SO₄).

In one embodiment of the present invention the method comprises, afterstep b), the step ii) of adding an aldehyde, a derivative of analdehyde, or a combination thereof to the dispersion formed in step b).In one embodiment of the present invention the derivative of an aldehydeis, paraformaldehyde or. In one embodiment of the present inventionalkalated lignin is reacted with an aromatic aldehyde, or glyoxal. Inone embodiment of the present invention the aromatic aldehyde isfurfuryl aldehyde. In one embodiment of the present invention thealdehyde is formaldehyde.

In one embodiment of the present invention the alkalated lignin isreacted with an aldehyde, e.g. formaldehyde, in order to formhydroxymethylated lignin. Allowing alkalated lignin to react with e.g.formaldehyde further increases the reactivity of lignin as hydroxymethylgroups are increased, which groups easily react with the other reactantcomponents during e.g. the resin cooking step.

In one embodiment of the present invention, in step ii), the weightratio of the aldehyde to lignin in the dispersion from step b) is0.2-0.7, and preferably 0.3-0.6.

The present invention further relates to lignin obtainable by the methodof the present invention. In one embodiment of the present invention thelignin obtainable by the method of the present invention can be lignin,which has been subjected to alkalation; to phenolation and alkalation;to alkalation and hydroxymethylation; or to phenolation, alkalation andhydroxymethylation.

The present invention further relates to a method for producing a bindercomposition, wherein the method comprises the step of:

(iii) cooking an aqueous composition comprising reactant componentsincluding lignin treated according to the present invention, apolymerizable substance and a crosslinking agent in the presence of acatalyst at a temperature of 60-95° C. for polymerizing the reactantcomponents until a binder composition with a predetermined viscosityvalue is formed.

In one embodiment of the present invention the lignin used in the methodfor producing a binder composition is lignin, which has been alkalatedaccording to the present invention. In one embodiment of the presentinvention the lignin used in the method for producing a bindercomposition is lignin, which has been phenolated and alkalated accordingto the present invention. In one embodiment of the present invention thelignin used in the method for producing a binder composition is lignin,which has been alkalated and hydroxymethylated according to the presentinvention. In one embodiment of the present invention the lignin used inthe method for producing a binder composition is lignin, which has beenphenolated, alkalated and hydroxymethylated according to the presentinvention.

In one embodiment of the present invention the predetermined viscosityvalue of the final binder composition is at least 40 cP, preferably atleast 50 cP, and more preferably at least 80 cP. In one embodiment ofthe present invention the predetermined viscosity value of the finalbinder composition is at least 40 but not more than 250 cP, preferablyat least 50 cP but not more than 150 cP, and more preferably at least 80but not more than 120 cP.

In one embodiment of the present invention the predetermined viscosityvalue of the final binder composition is at least 250 cP, preferably atleast 300 cP, and more preferably at least 500 cP. In one embodiment ofthe present invention the predetermined viscosity value of the finalbinder composition is at least 250 cP but not more than 1500 cP,preferably at least 300 cP but not more than 1200 cP, and morepreferably at least 500 but not more than 1000 cP. The viscosity ismeasured at 25° C. using a rotary viscometer. The predeterminedviscosity value of the final binder composition may vary depending onthe specific application where the binder composition is to be used.

The precise order of combining and/or adding the components needed forthe binder composition production may vary depending e.g. on therequired properties of the formed binder composition. The choice of thesequence of combining and/or adding the required components is withinthe knowledge of the skilled person. The precise amount of thecomponents used for producing the binder composition may vary and thechoice of the amounts of the different components is within theknowledge of the skilled person based on this specification. Thetemperature can be controlled during the production of the bindercomposition by cooling and/or heating the composition.

The essential feature of the binder production method is that thereactant components, e.g. lignin treated according to the presentinvention, the crosslinking agent and the polymerizable substance, areallowed to react with each other in an aqueous environment in thepresence of a catalyst and under heating such that the reactantcomponents are truly synthesized together and not just physically mixedtogether.

The method of the present invention surprisingly results in a moreenvironmentally friendly binder composition since in the binderproduction method the natural polymer lignin, which is a phenolicpolymer, has replaced at least part of the synthetic phenol substanceusually used in the production of phenolic compositions such as phenolformaldehyde resin. Without limiting the invention to any specifictheory about why the method of the present inventions results in theaforementioned advantage, it is to be considered that the suitability ofreplacing at least part of e.g. the phenol with lignin is due to thefact that lignin, the reactivity of which has been increased by themethod of the present invention, effectively react with an aldehyde,such as formaldehyde, in a quite similar manner as phenol.

In one embodiment of the present invention the aqueous compositionfurther comprises tannin as a reactant component.

In one embodiment of the present invention the tannin used originatesfrom any wood species. Tannin may originate from e.g. bark or heartwood.Quebracho tree, beech tree and wattle tree are presented as examples ofpossible sources of tannin. In one embodiment of the present inventionthe tannin used originates from softwood bark. In one embodiment of thepresent invention the tannin is separated from softwood bark ofdebarking units in sawmills or pulp mills. The separation process can becombined with an ethanol extraction process, a hot water extractionprocess, a hot steam extraction process or a water-ethanol extractionprocess of softwood bark. In one embodiment of the present invention thetannin is condensed tannin. Condensed tannin has a high dry content andis therefore suitable to be used in the present invention. The drymatter content of condensed tannin may vary between 40-100% and issuitably between 60-90% and preferably between 70-80%. Tannin with suchdry matter content can easily be dispersed, whereby a good reactivitywith the other reactant components is achieved. The tannin may also behydrolysable tannin.

In one embodiment of the present invention step (iii) comprises cookingthe composition preferably at a temperature of 65-90° C., and morepreferably at a temperature of 75-85° C.

In one embodiment of the present invention the crosslinking agent isselected from a group consisting of an aldehyde, a derivative of analdehyde, an aldehyde forming compound and combinations thereof. In oneembodiment of the present invention the derivative of an aldehyde ishexamethylenetetramine, paraformaldehyde or trioxane. In one embodimentof the present invention the crosslinking agent is selected from a groupconsisting of an aromatic aldehyde, glyoxal, furfuryl alcohol,caprolactam and glycol compounds. The aldehyde can be formaldehyde. Thearomatic aldehyde can be furfuryl aldehyde. In one embodiment of thepresent invention the crosslinking agent is a bio-based crosslinkingagent. In one embodiment of the present invention the crosslinking agentis an aldehyde, and preferably formaldehyde.

In one embodiment of the present invention the polymerizable substanceis selected from a group consisting of phenol, cresol, resorcinol andcombinations thereof. In one embodiment of the present invention thepolymerizable substance is phenol. In one embodiment of the presentinvention the polymerizable substance is selected from a groupconsisting of bio-based hydroxyphenols and their derivatives. In oneembodiment of the present invention the polymerizable substance is abio-based polymerizable substance. In one embodiment of the presentinvention the polymerizable substance is selected from a groupconsisting of lignin and tannin.

In one embodiment of the present invention the catalyst in step iii)comprises a salt or a hydroxide of an alkali metal. In one embodiment ofthe present invention the catalyst in step iii) is selected from a groupconsisting of sodium hydroxide, potassium hydroxide, acids and anymixture thereof. In one embodiment of the present invention the catalystin step iii) is sodium hydroxide.

In one embodiment of the present invention the relation between theamounts of lignin, catalyst/solvent, polymerizable substance, andcrosslinking agent, based on their dry contents, used for producing thebinder composition is the following: 18-weight-%, preferably 26-45weight-%, of cross-linking agent and catalyst/solvent, and82-30-weight-%, preferably 74-55 weight-%, of the polymerizablesubstance and lignin.

The present invention further relates to a binder composition obtainableby the method of the present invention.

The present invention further relates to an adhesive compositioncomprising the binder composition according to the present invention.The adhesive composition can further comprise one or more adhesivecomponents selected from a group consisting of other binders, extenders,additives, catalysts and fillers. A binder is a substance, which ismainly responsible for creating the growing and cross-linking of polymerand thus assists in the curing of polymer systems. An extender is asubstance, which assists the binder by adjusting physical properties forexample by binding moisture. The additive can be a polymer or aninorganic compound, which assists in properties like filling, softening,reducing costs, adjusting moisture, increasing stiffness and increasingflexibility. The catalyst is a substance, which usually boosts andadjusts the curing speed. By “substance” is herein to be understood asincluding a compound or a composition. The binder composition of thepresent invention may serve as a binder, an extender, an additive, acatalyst and/or a filler in the adhesive composition.

The present invention further relates to the use of the bindercomposition in an impregnation application, as a coating, forstrengthening plastic, for producing a compressed casting, a moulding, alaminate or a lacquer, or for gluing a wood product. The bindercomposition of the present invention can further be used for gluingcombinations of plastic and wood.

The present invention further relates to the use of the adhesivecomposition of the present invention for gluing a wood product.

In one embodiment of the present invention the wood product is selectedfrom a group consisting of a wood board, a wood veneer, and a wood bar.

In one embodiment of the present invention a layered composite structurecan be formed of two or more layers including at least one wood veneerlayer, wherein the layers are arranged the one above the other andcombined by means of gluing with the binder composition according to thepresent invention and/or the adhesive composition according to thepresent invention. In this specification, unless otherwise stated, theterm “wood veneer” is used to address a veneer, which can be formed ofany material, e.g. wood-based material, fiber material, compositematerial or the like. In this context, the thickness of the wood veneercan be varied. Typically the thickness of wood veneer is below 3 mm.

In one embodiment of the present invention the layered compositestructure is selected from a group consisting of a wood panel product, aplywood product, a composite product, and a pressed panel product. Thelayered composite structure can be formed of a number of layers,preferably wood veneer layers, in which the layers are laid one upon theother and glued together.

The embodiments of the invention described hereinbefore may be used inany combination with each other. Several of the embodiments may becombined together to form a further embodiment of the invention. Amethod, a composition or a use, to which the invention is related, maycomprise at least one of the embodiments of the invention describedhereinbefore.

An advantage of the method according to the present invention is thatthe reactivity of lignin e.g. separated from biomass can be markedlyincreased and also the heterogenic nature of lignin can be decreased.

An advantage of the present invention is that the reactivity of lignincan be increased by the method, and especially the alkalation step,according to the present invention. Lignin treated with the methodaccording to the present invention has an increased number of reactivegroups along the lignin structure compared to non-treated lignin.

An advantage of the method according to the present invention is that byusing lignin, the reactivity of which has been increased by the methodof the present invention, as a reactant component during the productionof a binder composition a more environmentally friendly bindercomposition is achieved. Surprisingly it has been found out that whenusing this kind of lignin as a reactant component the amount of thepolymerizable substance, such as the synthetic phenol substance, e.g.phenol, can be markedly decreased during the binder production process.As the phenol being a synthetic compound and lignin being a naturalpolymer, it is advantageous to be able to minimize the amount of phenolpresent in the final binder composition. The advantage of reducing theamount of synthetic materials is that a higher level of bio-basedcomponents is achieved in the final binder composition.

An advantage of the present invention is that by using lignin havingincreased reactivity compared to non-treated lignin, the properties ofthe final binder composition are more favorable for gluing applications.Lignin treated with the method according to the present inventionenhances curing, adhesion and tensile strength performance of the bindercomposition. An advantage of the present invention is that the gluingperformance of the binder composition or the adhesive compositionproduced is suitable for using the composition e.g. in exteriorapplications.

An advantage is that when using lignin, which has higher reactivity thannormal, non-treated lignin results in even better compatibility andreaction behavior of the binder production method according to thepresent invention.

EXAMPLES

Reference will now be made in detail to the embodiments of the presentinvention, an example of which is illustrated in the accompanyingdrawing.

The description below discloses some embodiments of the invention insuch a detail that a person skilled in the art is able to utilize theinvention based on the disclosure. Not all steps of the embodiments arediscussed in detail, as many of the steps will be obvious for the personskilled in the art based on this specification.

FIG. 1 illustrates a method according to some embodiments of the presentinvention for increasing the reactivity of lignin and the further use ofthe lignin.

FIG. 1 presents different combinations of treatment steps, which can beused for increasing the reactivity of lignin. FIG. 1 illustrates thephenolation step i), the alkalation steps a) and b) and thehydroxymethylation step ii) and their combinations for treating lignin.Lignin having increased reactivity compared to non-treated lignin can befurther used in synthesizing a binder composition, step iii) of FIG. 1,or it can be used for any other suitable application as illustrated inFIG. 1.

Before any of the treatment steps the source of lignin is chosen. Aspresented above, lignin can be selected from kraft lignin, biomassoriginating lignin, lignin from alkaline pulping process, lignin fromsoda process, lignin from organosols pulping, and combinations thereof.Also the other components and their amounts to be used in the methodaccording to the present invention are selected. If needed, thecomponents used in the method of FIG. 1 can be pretreated to be suitablefor the lignin treatment processes.

Following the various preparations and pretreatments, in one of theembodiments of the present invention shown in FIG. 1, step i) is carriedout. Step i) comprises reacting lignin with a compound selected from theclass of phenols in the presence of a catalyst. As a result of step i)of phenolation, reactive phenolic OH-groups are attached to thealiphatic portion of lignin.

After step i), step a) is to be carried out. Alternatively, the lignincan be directly treated according to step a) without firstly beingtreated in accordance with step i) as is illustrated in FIG. 1.

Step a) comprises forming an aqueous dispersion comprising alkali andlignin under heating. The alkali comprises a hydroxide of an alkalimetal. Then step b) is carried out by heating the formed dispersion at atemperature of 50-95° C. Step a) and step b) result in the lignin beingactivated through alkalation.

After step b) the alkalated lignin fraction can be introduced into thecooking step of the binder composition production method, during whichsaid lignin is polymerized with the other reactant components used inthe binder composition production method (step iii) of FIG. 1).

Alternatively the alkalated lignin from step b) can be further reactedwith an aldehyde in step ii) before being introduced into the synthesisof binder composition. Step ii) is carried out by adding e.g.formaldehyde into the dispersion of alkalated lignin from step b), whichresults in a hydroxymethylated product being formed.

As a result of step iii) a binder composition having desired propertiesand especially being for most parts based on biobased components isproduced. This binder composition can be used as such for gluingapplications or it can be further processed with other adhesivecomponents for producing an adhesive composition.

As above presented, in addition to using the alkalated lignin from stepb) or hydroxymethylated lignin from step ii) in a method for producing abinder composition, the alkalated lignin or hydroxymethylated lignin canbe used as such in any other suitable application.

Example 1 Alkalation

In this example the reactivity of lignin was increased by alkalating thelignin. The following components and their amounts were used:

concentration amount (g) water 836 NaOH 50% 584 lignin 75% 1270

Firstly, water and NaOH were mixed and heating of the mixture wasstarted. Then lignin was dispersed slowly into the mixture of alkali andwater with agitation and simultaneously the temperature was increased upto 60° C. When all of the lignin had been dispersed, the dispersion washeated at a temperature of about 75° C. for 1.5 hours. As a result thelignin became alkalated.

Lignin treated in accordance with Example 1 was thereafter used forproducing a binder composition. 38 g of phenol (90%) were mixed with 105g of alkalated lignin, after which 79 g of formaldehyde (37%) was addedin a stepwise manner. NaOH was used as catalyst. The temperature waskept under 75° C. Thereafter the cooking was continued at 85-90° C.until the viscosity of the formed composition was about 415 cp (asmeasured at a temperature of 25° C.).

The formed binder composition or resin was thereafter subjected to DSCmeasurements, the results of which can be seen in FIG. 2.

A comparative example 1 was formed by using lignin that had been treatedin the following manner:

The following components and their amounts were used:

concentration amount (g) water 836 NaOH 50% 584 lignin 75% 1270

Firstly, water and NaOH were mixed and heating of the mixture wasstarted. Then lignin was added into the mixture of alkali and water withagitation and simultaneously the temperature was increased up to 95° C.When the lignin had been added, the mixture was heated at a temperatureof about 90° C. for 1 hour.

Lignin from comparative example 1 was used for producing a comparativebinder composition 1 in a similar manner as above described. The formedcomparative binder composition was also subjected to DSC measurements.

The results from the DSC measurements of comparative binder composition1 are presented in FIG. 3.

As can be seen from FIG. 2, the binder composition formed by usinglignin alkalated according to the present invention shows only onedistinct peak. On the contrary, as can be seen from FIG. 3, thecomparative binder composition showed several peaks.

The distinct peak of FIG. 2 indicates that alkalated lignin has reactedwith phenol and formaldehyde forming a homogenous and uniform polymerstructure. The several distinct peaks in FIG. 3 indicate that phenol andformaldehyde react without a reaction with alkalated lignin or onlypartly together with alkalated lignin.

Without limiting the invention to any specific theory about whyalkalation of lignin in accordance with the present invention results inthis advantageous result, it is to be considered that lignin alkalatedin accordance with comparative example 1 remains in its originalparticle form or is agglomerated into larger clusters whereby thealkalation process is able to affect only the surface of such clustersor particles. Alkalation of lignin in accordance with the presentinvention results in lignin being well dispersed or dissolved when thealkalation process begins. As greater part or area of the lignin beingalkalated, the reactivity of lignin is increased compared to ligninalkalated in accordance with the process of the comparative example. Aslignin has an increased reactivity, it will easily react with the otherreactant components during the binder composition production.

Example 2 Alkalation, Low Temperature

In this example the reactivity of lignin was increased by alkalating thelignin. The following components and their amounts were used:

concentration amount (g) water 836 NaOH 50% 584 lignin 75% 1270

Firstly, water and NaOH were mixed and heating of the mixture wasstarted. Then lignin was dispersed slowly into the mixture of alkali andwater with agitation and simultaneously the temperature was increased upto 60° C. When all of the lignin had been dispersed, the dispersion washeated at a temperature of about 60° C. for about 1 hour. As a resultthe lignin became alkalated.

Example 3 Alkalation, High Temperature

In this example the reactivity of lignin was increased by alkalating thelignin. The following components and their amounts were used:

concentration amount (g) water 836 NaOH 50% 584 lignin 75% 1270

Firstly, water and NaOH were mixed and heating of the mixture wasstarted. Then lignin was dispersed slowly into the mixture of alkali andwater with agitation and simultaneously the temperature was increased upto 60-70° C. When all of the lignin had been dispersed, the dispersionwas heated at a temperature of about 90-95° C. for about 1 hour. As aresult the lignin became alkalated.

Example 4 Phenolation in Combination with Alkalation and Use of TreatedLignin for Producing a Binder Composition

In this example the reactivity of lignin was increased by phenolatingand alkalating the lignin, where after the treated lignin was used forproducing a binder composition.

Firstly the phenolation was performed. The following components andtheir amounts were used:

concentration amount (g) water 364 phenol 90% 381 lignin 98% 446 H₂SO₄96% 9

Water, phenol and lignin were mixed under agitation for about 5-10minutes after which H₂SO₄ was added. Then, the temperature was slowlyincreased up to 135° C. during a period of about 3 hour and kept at thattemperature for about one hour. Then the mixture was cooled and thetreatment ended resulting in phenolated lignin.

Then the phenolated lignin was alkalated. 430 g of phenolated lignin wasmixed with 150 g 50.0% NaOH under heating. Then the dispersion washeated at a temperature of 75° C. for about 1 hour.

As a result of the above treatments, phenolated and alkalated lignin wasformed.

After the phenolation and alkalation treatments, 38 g of water and 38 gof phenol (90%) were added to the composition, after which 368 g offormaldehyde (39.3%) was added in a stepwise manner. The temperature waskept under 75° C. Thereafter the cooking was continued at 85-90° C.until the viscosity of the formed composition was about 415 cp (asmeasured at a temperature of 25° C.).

Example 5 Alkalation in Combination with Hydroxymethylation and Use ofTreated Lignin for Producing a Binder Composition

In this example the reactivity of lignin was increased by alkalating andhydroxymethylating the lignin, where after the treated lignin was usedfor producing a binder composition. The following components and theiramounts were used:

water 220 g NaOH (first part, alkalation) 50% 146 g lignin 61% 752 gformaldehyde (first part, 514 g hydroxymethylation) 39.30% phenol 90%510 g formaldehyde (second part, 566 g binder formation) 39.30% NaOH(second part, 146 g binder formation) 50% NaOH (third part, 146 g binderformation) 50%

Firstly, water and NaOH were mixed and heating of the mixture wasstarted. Then lignin was dispersed slowly into the mixture of alkali andwater with agitation and simultaneously the temperature was increased upto about 75° C. When all of the lignin had been dispersed, thedispersion was heated at about 75° C. for about 1 hour. As a result thelignin became alkalated. Then formaldehyde was added to the dispersionand the reaction was allowed to continue for about 1 hour resulting inthe lignin being hydroxymethylated.

The treated lignin was used for producing a binder composition. Thephenol was added to the composition, followed by the addition offormaldehyde and then NaOH. Cooking of the formed composition wascontinued, with addition of NaOH, at a temperature of 70-90° C. untilthe viscosity of the formed composition was about 300 cp (as measured ata temperature of 25° C.).

Example 7 Preparing an Adhesive Composition

In this example the binder composition produced in Example 4 was usedfor the production of an adhesive composition. The binder compositionwas mixed with extenders, fillers, catalysts, additives, as examples ofwhich e.g. starch, wood flour and hardener (e.g. tannin or carbonates)can be mentioned, thus forming the adhesive composition.

Example 8 Applying the Binder Composition for Producing a PlywoodProduct

Wood veneers having the thickness of below 3 mm were glued together withthe binder composition produced in Example 5 for producing a 7-plywood.Results showed that the gluing effect was sufficiently good for gluingwood veneers.

Example 9 Applying the Adhesive Composition for Producing a PlywoodProduct

In this example the adhesive composition of Example 7 was applied ontowood veneers. The wood veneers were joined together by the adhesivecomposition for forming a plywood. The dry matter content of theadhesive composition was between 45 and 55%. The wood veneers with theadhesive composition were pressed by hot-pressing technique at atemperature between 120-170° C. The adhesive composition wassimultaneously cured. The adhesive composition of the present inventionwas found suitable for gluing wood veneers together and thus formanufacturing plywood.

Example 10 Applying the Binder Composition for Producing Laminates

In this example the binder composition as produced in Example 4 was usedin an impregnation application. During the production of laminates paperwas impregnated with an alcohol solution of the binder composition,after which the impregnated layers were transferred into a furnace. Thealcohol was volatilized and the binder composition was partly cured. Thelayers comprising such semi-cured composition were arranged the oneabove the other and baked by a hot-pressing technique in order to formuniform thicker boards or laminates.

In the binder production method presented in the examples above, phenoland formaldehyde are used. However, any other polymerizable substance orcross-linking agent can be equally well used in the binder compositionproduction method as will be obvious for the skilled person based onthis specification.

It is obvious to a person skilled in the art that with the advancementof technology, the basic idea of the invention may be implemented invarious ways. The invention and its embodiments are thus not limited tothe examples described above; instead they may vary within the scope ofthe claims.

1. A method for increasing the reactivity of lignin, wherein the method comprises the following steps: a) forming, under heating at a temperature of 30-70° C., an aqueous dispersion comprising alkali and lignin, wherein the alkali comprises a hydroxide of an alkali metal; and b) heating the dispersion formed in step a) at a temperature of 50-95° C. for producing alkalated lignin.
 2. The method of claim 1, wherein the concentration of alkali is 5-50 weight-%, and preferably 10-25 weight-% based on the total weight of the dispersion in step a).
 3. The method of claim 1, wherein the concentration of lignin is 10-50 weight-%, preferably 20-50 weight-%, and more preferably 20-45 weight-% based on the total weight of the dispersion in step a);
 4. The method of claim 1, wherein the temperature in step a) is preferably 50-65° C.
 5. The method of claim 1, wherein the temperature in step b) is preferably 60-75° C.
 6. The method of claim 1, wherein step b) is carried out for 15 minutes-24 hours, preferably for no longer than 5 hours, and more preferably for 0.5-1.5 hours.
 7. The method of claim 1, wherein the method comprises, before step a), the step i) of reacting lignin with a compound selected from the class of phenols.
 8. The method of claim 7, wherein step i) is carried out at a temperature of 100-140° C. for 1-3 hours in the presence of a catalyst.
 9. The method of claim 1, wherein the method comprises, after step b), the step ii) of adding an aldehyde, a derivative of an aldehyde, or a combination thereof to the dispersion formed in step b).
 10. The method of claim 9, wherein the weight ratio of the aldehyde to the lignin in the dispersion from step b) is 0.2-0.7, and preferably 0.3-0.6.
 11. The method of claim 9, wherein the aldehyde is formaldehyde.
 12. Lignin obtainable by the method of claim
 1. 13. A method for producing a binder composition, wherein the method comprises the step of: (iii) cooking an aqueous composition comprising reactant components including lignin obtainable by the method of claim 1, a polymerizable substance and a crosslinking agent in the presence of a catalyst at a temperature of 60-95° C. for polymerizing the reactant components until a binder composition with a predetermined viscosity value is formed.
 14. The method of claim 13, wherein step (iii) comprises cooking the composition preferably at a temperature of 65-90° C., and more preferably at a temperature of 75-85° C.
 15. The method of claim 13, wherein the crosslinking agent is an aldehyde, and preferably formaldehyde.
 16. The method of claim 13, wherein the polymerizable substance is selected from a group consisting of phenol, cresol, resorcinol and combinations thereof.
 17. The method of claim 13, wherein the catalyst is selected from a group consisting of sodium hydroxide, potassium hydroxide and any mixture thereof.
 18. A binder composition obtainable by the method of claim
 13. 19. An adhesive composition comprising the binder composition of claim
 18. 20. The use of the binder composition of claim 18 in an impregnation application, as a coating, for strengthening plastic, for producing a compressed casting, a laminate or a lacquer, or for gluing a wood product.
 21. The use of the adhesive composition of claim 19 for gluing a wood product. 